/*
 * Nextcloud Talk - Android Client
 *
 * SPDX-FileCopyrightText: 2024 Julius Linus <juliuslinus1@gmail.com>
 * SPDX-License-Identifier: GPL-3.0-or-later
 */

package com.nextcloud.talk.data.network

import android.content.Context
import android.net.ConnectivityManager
import android.net.Network
import android.net.NetworkCapabilities
import android.net.NetworkRequest
import android.net.NetworkRequest.Builder
import androidx.core.content.getSystemService
import androidx.core.os.trace
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.channels.awaitClose
import kotlinx.coroutines.flow.Flow
import kotlinx.coroutines.flow.callbackFlow
import kotlinx.coroutines.flow.conflate
import kotlinx.coroutines.flow.distinctUntilChanged
import kotlinx.coroutines.flow.flowOn
import javax.inject.Inject
import javax.inject.Singleton

@Singleton
class NetworkMonitorImpl @Inject constructor(
    private val context: Context
) : NetworkMonitor {
    override val isOnline: Flow<Boolean> = callbackFlow {
        trace("NetworkMonitorImpl.callbackFlow") {
            val connectivityManager = context.getSystemService<ConnectivityManager>()
            if (connectivityManager == null) {
                channel.trySend(false)
                channel.close()
                return@callbackFlow
            }

            /**
             * The callback's methods are invoked on changes to *any* network matching the [NetworkRequest],
             * not just the active network. So we can simply track the presence (or absence) of such [Network].
             */
            val callback = object : ConnectivityManager.NetworkCallback() {

                private val networks = mutableSetOf<Network>()

                override fun onAvailable(network: Network) {
                    networks += network
                    channel.trySend(true)
                }

                override fun onLost(network: Network) {
                    networks -= network
                    channel.trySend(networks.isNotEmpty())
                }
            }

            trace("NetworkMonitorImpl.registerNetworkCallback") {
                val request = Builder()
                    .addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)
                    .build()
                connectivityManager.registerNetworkCallback(request, callback)
            }

            /**
             * Sends the latest connectivity status to the underlying channel.
             */
            channel.trySend(connectivityManager.isCurrentlyConnected())

            awaitClose {
                connectivityManager.unregisterNetworkCallback(callback)
            }
        }
    }
        .distinctUntilChanged()
        .flowOn(Dispatchers.IO)
        .conflate()

    private fun ConnectivityManager.isCurrentlyConnected() =
        activeNetwork
            ?.let(::getNetworkCapabilities)
            ?.hasCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET) ?: false
}
